Effects of iron substitution for nickel on electrochemical properties of LiNi0.8Co0.2O2 for lithium rechargeable batteries

iron was substituted for Ni in LiNi0.8Co0.2 in order to enhance its electro chemical properties such as cycle life and rate capability. LiNi0.8-xFexCo0 .2O2 (0 less than or equal to x less than or equal to 0.1) wag synthesized in flowing oxygen, for 12-48 h at 650-800 degreesC, and its structural and electrochemical properties were characterized with X-ray diffraction (XRD), cyclic voltammetry (CV) and charge-discharge tests. The XRD patterns of Li Ni0.8-xFexCo0.2O2 showed that the alpha -NaFeO2 type layered structure was maintained up to x = 0.1. As Fe was substituted for Ni up to x = 0.05, the rate capability of LiNi0.8-xFexCo0.2O2 was improved. LiNi0.75Fe0.05Co0.2O2 showed better cycle stability than LiNi0.8Co0.2O2. XRD measurements indicat ed that the lattice Of LiNi0.75Fe0.05Co0.2O2 expanded less than that of LiN i0.8Co0.2O2 when the lithium was de-intercalated. CV curves of LiNi0.8-xFex Co0.2O2 showed current peaks, which are related to the phase transitions, d iminished with Fe substitution during charging and discharging owing to the decrease of Ni3+. Consequently, the improved cycle stability of LiNi0.75Fe 0.05Co0.2O2 May be attributed to the decrease of phase transition. (C) 2001 Elsevier Science B.V. All rights reserved.